"Graffiti is something that's done on the spot, with the traditional tools," Brennan said. "Street art is generally premeditated. It's done in the studio and brought to the street, or it's done with the intention of being installed, and it's not so much concerned with the fame and the game that goes along with graffiti."

The two street art experts tagged the San Francisco scene as bold for its willingness to try different things and its use of pop culture in its pieces.

"There's a little more of a quirkiness here," Rotman said. "And risk taking with what people are willing to put up. People don't get clowned on as much if you do something weird. So that's kinda neat, 'cause you see more variety."

"There are plenty of people out there that just assume graffiti is gang related in some way, or it's the same people that are out there robbing people, or whatever," Brennan said. " Probably has a lot to do with what's-his-name running for governor."